A. When you start your computer, the system first checks the C drive, so if you place a program called explorer.exe on the root of C, the system uses that program rather than the one in %systemroot% (e.g., c:\winnt). This behavior occurs because the shell value (under HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon) simply says "explorer.exe." If you edit the registry to make this value c:\winnt\explorer.exe, this behavior won't occur because you've specified the search path in the value.
Microsoft will provide a fix for this problem in Windows 2000 Service Pack 2 (SP2). If you need a fix now, download the August 17, 2000, Security Update via Windows Update or from the Microsoft Web site.
In addition, check out Microsoft article Q269049 for a Windows NT fix.